Accuracy Study of Kato-Katz and Helmintex Methods for Diagnosis of Schistosomiasis Mansoni in a Moderate Endemicity Area in Sergipe, Northeastern Brazil

Abstract

Schistosomiasis is a neglected tropical disease (NTD) caused by blood flukes from the genus Schistosoma. Brazil hosts the main endemic area in the Americas, where Schistosoma mansoni is the only species causing the disease. Kato-Katz (KK) thick smear is the WHO recommended screening test for populational studies, but there is growing evidence for the sensitivity limitations associated with KK, especially in areas with low parasite loads. Helmintex (HTX) is another highly sensitive egg-detection method, based on the magnetic properties of S. mansoni eggs and their isolation in a magnetic field. The objective of this study is to evaluate both KK and HTX in a moderate endemic locality, Areia Branca, located in the municipality of Pacatuba, in the state of Sergipe in northeastern Brazil. From 234 individual fecal samples, two KK thick smears were prepared and evaluated for each sample. Similarly, 30 g of each fecal sample was processed by HTX protocol. Eggs were detected in 80 (34.18%) residents. Twenty-three (9.83%) samples were positive for eggs (only by KK), and 77 (32.91%) samples showed positive for eggs (only by HTX). Sensitivity, specificity, and accuracy estimates gave values of 28.75%, 100% and 75.64%, respectively, for KK, and 96.25%, 100% and 98.72% respectively, for HTX. The positive predictive value was 100% for both methods, while the negative predictive value was 72.99% for KK and 98.09% for HTX. Overall, HTX presented a superior performance compared to the one sample, two slides KK examination. The study confirms the role of HTX as a reference method for the definition of true-positive samples in comparative accuracy studies and its potential role in the late stages when the certification of schistosomiasis transmission interruption is required. Diagnostic tests are important tools for the elimination of this NTD, besides the effective implementation of safe water, basic sanitation, snail control, and the treatment of infected populations.

Diagnostic tests for human Schistosoma mansoni and Schistosoma haematobium infection: a systematic review and meta-analysis

“…The original research articles were on point-of-care CCA (two articles), CRISPR (one article), multidiagnostic microscope (one article), and Helminthex (one article). 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 These articles might have added some value to our comparisons based on CCA, CAA, and Helminthex. One research study was done in Ontario, Canada.…”

“… 153 Since we finalised our analyses, we checked for new studies and found that nine that met our inclusion criteria were published between Jan 1 to April 23, 2023, of which two were reviews 154 , 155 and seven original research articles. 156 , 157 , 158 , 159 , 160 , 161 , 162 , 163 The two reviews were a meta-analysis evaluating the accuracy of antigen, antibody, and molecular tests for S mansoni and S haematobium only that did not use Bayesian latent class models, and a scoping review on proteins for antibody-based tests. The original research articles were on point-of-care CCA (two articles), CRISPR (one article), multidiagnostic microscope (one article), and Helminthex (one article).…”

Identification ofSchistosoma haematobiumandSchistosoma mansonilinear B-cell epitopes with diagnostic potential usingin silicoimmunoinformatic tools and peptide microarray technology

“…For urogenital schistosomiasis, the urine filtration technique is the standard diagnostic method and for intestinal schistosomiasis, the Kato Katz technique is the standard diagnostic method (6)(7)(8). In addition to high specificity (7,9), both techniques have minimal operational costs (the test kits are inexpensive), low complexity and they are relatively easy to perform in resource-limited field settings (6,8,9). Moreover, prepared Kato Katz slides can be stored for months at room temperature for later microscopic examination.…”

“…The sensitivity of the techniques is limited by the host infection intensity, daily variation of schistosome egg excretion and uneven distribution of eggs within stool specimens (11). Additionally, both methods are unable to diagnose recent infections (for instance, in cases where worms have not yet started to produce eggs) or single worm/sex infections and the Kato Katz technique is unable to analyse watery stool specimens (9). The lack of sensitivity especially in low endemic areas and after successful control interventions lead to underestimation of true schistosomiasis prevalence in such settings (7–10).…”

“…The lack of sensitivity especially in low endemic areas and after successful control interventions lead to underestimation of true schistosomiasis prevalence in such settings (7–10). Moreover, undetected and untreated individuals may continue schistosomiasis transmission by contaminating fresh water sources with urine and faeces containing schistosome eggs (1,9). Due to the numerous disadvantages associated with the microscope based techniques, the use of other methods like molecular detection, circulating cathodic antigen (CCA), circulating anodic antigen (CAA) has gathered pace (8).…”